pv-datera-2   100Gi      RWO           Available                                              7s

pv-datera-3   100Gi      RWO           Available                                              4s


[root@tlx241 /]# kubectl get pvc

NAME                     STATUS    VOLUME        CAPACITY   ACCESSMODES   AGE

pv-claim-test-petset-0   Bound     pv-datera-0   0                        3m

pv-claim-test-petset-1   Bound     pv-datera-1   0                        3m
  ```



A pod can use a PersistentVolume Claim like below:



 ```
apiVersion: v1

kind: Pod

metadata:

  name: kube-pv-demo

spec:

  containers:

  - name: data-pv-demo

    image: nginx

    volumeMounts:

    - name: test-kube-pv1

      mountPath: /data

    ports:

    - containerPort: 80

  volumes:

  - name: test-kube-pv1

    persistentVolumeClaim:

      claimName: pv-claim-test-petset-0
  ```



The result is a pod using a PersistentVolume Claim as a volume. It in-turn sends the request to the Datera volume plugin to provision storage in the Datera Data Fabric.




 ```
[root@tlx241 /]# kubectl describe pods kube-pv-demo

Name:       kube-pv-demo

Namespace:  default

Node:       tlx243/172.19.1.243

Start Time: Sun, 14 Aug 2016 19:17:31 -0700

Labels:     \<none\>

Status:     Running

IP:         10.40.0.3

Controllers: \<none\>

Containers:

  data-pv-demo:

    Container ID: [docker://ae2a50c25e03143d0dd721cafdcc6543fac85a301531110e938a8e0433f74447](about:blank)

    Image:   nginx

    Image ID: [docker://sha256:0d409d33b27e47423b049f7f863faa08655a8c901749c2b25b93ca67d01a470d](about:blank)

    Port:    80/TCP

    State:   Running

      Started:  Sun, 14 Aug 2016 19:17:34 -0700

    Ready:   True

    Restart Count:  0

    Environment Variables:  \<none\>

Conditions:

  Type           Status

  Initialized    True

  Ready          True

  PodScheduled   True

Volumes:

  test-kube-pv1:

    Type:  PersistentVolumeClaim (a reference to a PersistentVolumeClaim in the same namespace)

    ClaimName:   pv-claim-test-petset-0

    ReadOnly:    false

  default-token-q3eva:

    Type:        Secret (a volume populated by a Secret)

    SecretName:  default-token-q3eva

    QoS Tier:  BestEffort

Events:

  FirstSeen LastSeen Count From SubobjectPath Type Reason Message

  --------- -------- ----- ---- ------------- -------- ------ -------

  43s 43s 1 {default-scheduler } Normal Scheduled Successfully assigned kube-pv-demo to tlx243

  42s 42s 1 {kubelet tlx243} spec.containers{data-pv-demo} Normal Pulling pulling image "nginx"

  40s 40s 1 {kubelet tlx243} spec.containers{data-pv-demo} Normal Pulled Successfully pulled image "nginx"

  40s 40s 1 {kubelet tlx243} spec.containers{data-pv-demo} Normal Created Created container with docker id ae2a50c25e03

  40s 40s 1 {kubelet tlx243} spec.containers{data-pv-demo} Normal Started Started container with docker id ae2a50c25e03
  ```



The persistent volume is presented as iSCSI device at minion node (tlx243 in this case):



 ```
[root@tlx243 ~]# lsscsi

[0:2:0:0]    disk    SMC      SMC2208          3.24  /dev/sda

[11:0:0:0]   disk    DATERA   IBLOCK           4.0   /dev/sdb


[root@tlx243 datera~iscsi]# mount  ``` grep sdb

/dev/sdb on /var/lib/kubelet/pods/6b99bd2a-628e-11e6-8463-0cc47ab41442/volumes/datera~iscsi/pv-datera-0 type xfs (rw,relatime,attr2,inode64,noquota)
  ```



Containers running in the pod see this device mounted at /data as specified in the manifest:



 ```
[root@tlx241 /]# kubectl exec kube-pv-demo -c data-pv-demo -it bash

root@kube-pv-demo:/# mount  ``` grep data

/dev/sdb on /data type xfs (rw,relatime,attr2,inode64,noquota)
  ```



**Using Pet Sets**



Typically, pods are treated as stateless units, so if one of them is unhealthy or gets superseded, Kubernetes just disposes it. In contrast, a PetSet is a group of stateful pods that has a stronger notion of identity. The goal of a PetSet is to decouple this dependency by assigning identities to individual instances of an application that are not anchored to the underlying physical infrastructure.